Manhole Control

City of FayettevilleFor many municipalities, manhole rehabilitation often takes a back seat to sewer mainline rehabilitation. For Fayetteville, N.C.’s Public Works Commission (PWC), it’s just as important.

Typically, manhole rehabilitation is an add-on for pipe lining projects and usually involves a simple solution for an all-problems specification. In many cases this works well, but good products can fail, good companies can make mistakes and resources can be wasted. Each manhole is an independent structure within a large network that needs to be addressed individually. In lining pipes, the lines are usually inspected and major issues identified before rehabilitation starts. The same process is needed for manholes for a consistent successful long-term rehabilitation.  

Rehabilitation of manholes is much more than repairing corrosion and stopping active infiltration – it needs to stop corrosion and prevent infiltration. To do this, the correct technologies need to be selected. On some projects, this may involve the use of one product for the majority of the manholes with a select few that need special attention. This situation usually only exists in sewer districts with relatively simple terrain and a low risk for infiltration. The City of Fayetteville does not fit within this scenario.

City of FayettevilleCity of Fayetteville

Fayetteville’s sewer system includes more than 1,200 miles of sewer lines, more than 30,000 manholes and 69 lift stations. This infrastructure serves a population of roughly 218,000, producing an average flow of 24.4 million gallons per day (gpd). With lakes, swamps and a river throughout the hilly city, there is a significant threat from H2S corrosion and infiltration. The City’s PWC made the decision to use two different technologies to address the rehabilitation of the manholes, allowing it to get the most value from its investment and get a rehabilitation that will work in the long term.

Writing a specification for manhole rehabilitation is about more than just selecting products. It is about selecting the right technology. Today, most manhole rehab products that are available can be categorized by three groups or types of technology: cementitious, polymer and cured-in-place/fiber reinforced. Each of these has their pros and cons and not one is necessarily the best fit for every situation. Cementitious liners are an effective, low-cost structural solution for structures with little to no infiltration suffering from low exposure to corrosion. A polymer liner is a moderate cost solution that is not structural, but can withstand high levels of corrosion exposure and little to no infiltration. Cured-in-place liners are the highest cost option, but can withstand both high levels of corrosion and infiltration.

Application Process

Fayetteville’s PWC chose to use a cementitious material for restoring the manholes, coated with a polymer coating or a cured-in-place liner for their rehabilitation needs. The products used by the contractor, Mechanical Jobbers, were Protective Liner Systems’ PerpetuCrete MSC for the cementitious liner, its PerpetuCoat M for the polymer and its PerpetuWall system for the cured-in-place liner.

Both products are applied using the same process, which begins with cleaning the structure and stopping infiltration. Next, each manhole gets restored to as-built condition using PerpetuCrete MSC. PerpetuCoat M is either spray- or hand-applied, depending on what works best for the contractor. PerpetuWall’s installation involves layering epoxy and fiberglass to build a fiberglass-reinforced liner. The epoxy layers can also be spray- or hand-applied, but the fiberglass cloth must be installed by hand. The cure time is about four hours for both products. Manholes can immediately be put back into service with the exception of high-flow manholes and similar structures, which may take an additional one to two hours.

Mechanical Jobbers has been awarded the various annual contracts to rehabilitate manholes in Fayetteville’s sewer rehab project since 2007. Protective Liner Systems’ products have been in the project specifications since 2006. To date, the City has had nearly 300 manholes rehabilitated with about 75 percent using the cured-in-place liner.

Keys to Project Success

Several factors generally contribute to the success of a large scale rehabilitation project, and effective communication is often at the top of the list. With good project specifications in place, communication between the city, the public, the contractor and the manufacturer is essential for getting work completed in a safe and timely manner without sacrificing quality.

Fayetteville’s manhole rehab project was no exception. Monthly progress meetings helped keep the PWC, Mechanical Jobbers and Protective Liner Systems on the same page. The meetings gave each party an opportunity to address concerns, plan for the next month and keep an ongoing face-to-face relationship to support teamwork. In addition, the PWC also had an inspector onsite to help keep the project moving smoothly. As problems or issues came up that required approval or a decision from the City, the inspector could address the issues onsite. This workflow process helped avoid dozens of phone calls that can often waste time in solving simple problems.

Infiltration and Other Challenges

Problem solving is the biggest part of getting work done in the rehab business. The further away manholes are from roadways, the bigger and more frequent the problems become. Most of the manholes that needed repair in Fayetteville were in neighborhoods, outfalls, lakes or swamps. The structures in outfalls posed some challenges but most were lined without any problems. In some cases, boats and air boats were required to access manholes due to their remote location. The manholes’ proximity to the water also meant that infiltration was difficult to fight.   

Protective Liner Systems always specifies, regardless of the product used, that all infiltration must be stopped before lining a structure. The thinking is that without stopping the infiltration, the product cannot have an opportunity to form and produce the protection that it promises. In Fayetteville, stopping infiltration and using unorthodox tools to reach manholes were, at times, a logistical challenge as plans had to be changed on the fly while keeping within a planned work schedule. A relatively strict schedule was also required due to many of the off-road structures being located in outfalls that had to be accessed through private property.

Working on private property is always challenging and requires more than just communicating the presence of crews. Most of the public never thinks twice about the utilities underground, but manholes are a nuisance on the property to hide or avoid. Typically, when a crew arrives to complete work, the manhole is not in a place where a large truck can easily get access to without causing damage to property. Having products that require very little equipment onsite helps to reduce or eliminate damage to private property and keeps everyone happy. In Fayetteville, the PWC did not have to deal with a large volume of complaints and the contractor was able to complete work without having to go back and repair damage to landscaping. This is always an important consideration for contractors that is frequently overlooked.

Summing It Up

When performing manhole rehab, the right product must be practical for use in the field as well as meet the performance needs required to rehabilitate the structure. Although it may be faster, spraying cementitious or polymer materials requires large equipment at times and can be messy, noisy and a general nuisance. Communicating with the public is also key. Going from house to house to rehabilitate manholes makes it easier to convince a homeowner that the work will in no way harm their landscaping. Good communication, the right products and quality work make these projects run smoothly.

Every manhole is different from the next. Manholes can be located just about anywhere one could imagine. In Fayetteville, the variety of locations where manholes were found made it difficult for the contractor.  With a well thought out specification, effective communication between the system owner, contractor, manufacturer and public, these difficulties were overcome. The specification made it clear to Mechanical Jobbers what the rehabilitation work was trying to accomplish. The products selected were able to meet the technical needs for the rehabilitation to work, while at the same time, working well in odd situations.

Joseph Trevino is the vice president of Protective Liner Systems Inc.
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